Flashlamp contaminant detector



Oct. 16, 1956 F. w. HARJES ETAL 2,767,325

FLASHLAMP CONTAMINANT DETECTOR Filed April 26, 1952 v INVENTORS .J. WARREN CULP I I P: ALZ 4. 077/! BY 4/)? PRESSURE g Bf ATTORN United States Patent FLASHLAMP CONTAMINANT DETECTOR Frederick William Harjes, Kew Gardens Hills, Norman vP. Salz, Bayside, and John Warren Culp, Flushing, N. Y., assignors to Sylvania Electric Products, Inc, a corporation of Massachusetts Application April 26, 1952, Serial No. 284,662

9 Claims. (Cl. 25083.3)

This invention relates to a method and apparatus for the detection of contaminating gases within a sealed container. More particularly, it relates to a method and apparatus for detecting and measuring air as a contaminant in oxygen filled flash lamps.

In view of the fact that oxygen is present in flash lamps at pressures substantially less than atmospheric, usually in the neighborhood of from 37 to 58 cm. of mercury pressure depending on the lamp size, the lamps are prone to suck in any atmospheric gases if the lamps are not hermetically sealed. This is true even with very small cracks or leaks in the seal or envelope portions of the lamp. When such leaks occur the lamps are likely to explode when flashed in view of the high pressure which is developed when inert gases such as nitrogen which do not enter the reactions are heated by the combustion of the light giving material. For this reason it has been quite a common custom to test the completed lamps for the presence of air. Inasmuch as even small leaks may result in an appreciable increase in pressure over a long period of time such as would be the case when bulbs are kept on the shelf for some time before firing it hasbeen the custom to make such tests after the expiration of several days after the bulbs have been completed. One well known method for conducting such a test is to excite the gases within the lamp with the aid of a standard high frequency coiler such as is customarily used in vacuum work. A blue green color of this discharge indicates a good lamp. One that has a purplish color, however, indicates the presence of atmospheric air. It is essential to use moistened electrodes pressed against the glass to insure good electrical contact and minimized air breakdown between the electrode and the lamp which, if it occurs, obscures the discharge. In this test the brightness of the discharge is so low that it must be observed in total darkness. Furthermore, the brightness is a function of such variables as electrode dampness, pressure of the gas within the bulb, contamination of the oxygen inside the bulb, and voltage across the electrodes. It is, therefore, diflicult to see small variations of color under these circumstances. This method also has the serious drawback that the high frequency coiler occasionally flashes a bulb in front of the operators dark adapted eyes. This not only disrupts the test program until the eye again becomes adapted to darkness but also causes a contraction of the iris which might in time cause considerable eye damage.

It is therefore, an object of this invention to provide a method and apparatus by means of which small contaminations can be detected and measured by a nondestructive method.

It is a further object of this invention to provide a method and apparatus which is mechanical and which has a high degree of sensitivity.

It has been found that in view of the fact that the spectral distribution of light from a gaseous discharge within a photoflash lamp is altered in the presence of air small contaminating quantities of foreign gases can be ice measured accurately by permitting the light from the glowing flash lamp to fall on the cathode of a photomultiplier tube through an arrangement which will intermittently filter out certain light rays.

In the drawings which illustrate an embodiment of the method and apparatus of this invention;

Figure l is a schematic view showing the source of energy to induce the radio frequencydischarge within a flash lamp, a pair of electrodes and a flash lamp in position therebetween;

Figure 2 is a front elevation partly in section showing the positions of a phototube, a revolving drum, a switch and motor;

Figure 3 is a preferred embodiment of a circuit diagram, and;

Figure 4 is a graph showing the curve obtained by plotting air pressure against resistance.

The non-destructive method of detecting and measuring air as a contaminant in oxygen filled flash lamps of this invention differs primarily from the method of the prior art in that a sensitive photomultiplier tube provided with a means for alternately scanning the total light output of the discharge and the light output less the ultraviolet rays is substituted for the eye of the observer.

The apparatus of this invention consists essentially of a means for generating high frequency energy, electrodes connected therewith, a phototube, and means for measuring the intensity and spectral character of a glow discharge.

The means for generating high frequency energy may consist of an oscillator such as shown at 10. This oscillator is adapted to produce energy of the type which will introduce a gaseous discharge within a flash lamp when electrodes such as 12 connected to the oscillator are placed in intimate contact with the envelope 14 of the,

flash lamp 16. These electrodes are preferably made of a sponge-like material having good current carrying characteristics.

The means for detecting and measuring the intensity and spectral character of the glow discharge may, for example, consist of a photomultiplier tube, means for intermittently filtering the light rays which strike the cathode of a photo tube and a bridge circuit connected therewith. In the embodiment illustrated in the drawings the means for intermittently filtering the light is shown as a rotating drum 22 which is provided with two apertures one of which is covered with an ultraviolet absorbing gelatin filter 24. The rotatable drum 22 must naturally be provided with some means for rotation. This may be 7 in the nature of a motor 30 connected to the drum 22 by means of a shaft 32. In order that the photo tube 20 can measure the light passing through the aperture provided with filter 24 and compare the two with one another a commutator switch 34 is mounted on shaft 32. This switch, can naturally be replaced with any other switch capable of doing a similar job. In the preferred embodiment of the apparatus of this invention drum 22 is rotated at a speed of about 1800 R. P. M. During the measurement of a gaseous discharge through lamp 16 the photo tube has two alternate current components, one representing the total light output of the gaseous discharge and the other representing the visible light or the total light less the light absorbed by the ultraviolet absorbing filter 24. In order to properly evaluate the two currents the switch 34 mountedon the shaft 32 switches the two components synchronously to two branches of a bridge circuit as shown in Figure 3. The circuit consists of two photo tube load resistors R1 and R2 and a galvanometer G. The smaller current component, corresponding to the visible light output, is switched to a fixed resistor R1 (e. g. 1 megohm) and the larger current component, corresponding to the total light ofthe -gaseousedischarge; isswitched to a variable resiston-RZ (e. gr.vl fmegohm) The mariable resistor is-- adjusted until the galvanometer reaches zero current indicating that the average voltage drops across the two resistors-are equal and hence thettwo resistors havethe= 5 sametratio as the two components -ofcurrent. The value oLthesvariable resistance isatherefore a lmeasure-of- -the 4 degree of air contaminationofl-theflashlarnp;

Figure 14 of. the drawings shows a curve which has been obtained by plotting thevalues of RZ obtained fon-vary ing amounts-of air pressure-in-- centimeters-ofmercury withinra flashdamp. Thisac'urvecan be referred to if so 1 desired in determining the amount =o---air-present in any selected bulb.

In practice the system-of this invention mayreadily be 15 used to indicate whethenair pressure in a 'sel'ectedbulb is greater or less than a chosen tolerance level by setting the variable resistance to correspond to the chosenpressure. The galvanometer will then show a positive ora negativedeflection according to whether; the pressure 0 is larger or smaller than the-tolerance;1evel= From this it is readily understandable thatthe galvanometermight" readily bereplaced by a-device which would -be actuated; toperformone function when-theideflection-would betothe left and another--function when the -deflection is to the' right; and thus, forexampiaact -to sort 1 bulbs with permissible pressure from those-where -the-pressure--- is excessive.

It has beenfound 'thatthe above-described method of air contaminationdetection is much more sensitive than any of the old-methods. Bythis method'it-ispossible to" detect :centimeter ofair as opposed-to -thelimit-of 2 centimeters by the old method. The new apparatus-is so much morev sensitive than apparatusand procedures heretofore used that it can be used-to check=;bu1bs-as they" come 0E ithe production line thus; enabling the'operator' to I become aware of faultytechniquesor equipment; promptly and'thus prevent the-production oflarge quantities of poor grade bulbs.- It alsohas- ;thefurther ad-- vantages of eliminating human error which is inherent 'in 40 visual. detection. i v

From the foregoing, it will be appreciated-that there is provided in accordance with. this invention apparatus for measuring the concentration of air-Within the enclosed space 14having agaseous which includes a .15 high-frequency source 10 for producing a glow discharge within-theenclosed space, a'phototube 20-positioned to intercept; the light 'rays emitted from the; enclosed space, a rotatable filteringmeans 22,24 interposed'bel tween saidenclosed-space and; said photo-tube for inter- 5O mitteut-ly filtering out any ultraviolet radiations emitted from the enclosed space whereby said photo tube provides one currentcomponenbcorresponding tothe total light outputof said glowdischarge and a further current t componentcorresponding to the visible; light output ofsaid glow discharge, a measuringcircuit including bridge or measuring arms R1, R2, and switcher commutator means- 34operable in substantial synchronism With the filtering means and connected between the phototube and v the measuring circuit? 7 i i While the above description and "drawings submitted herewith disclose a preferred-and practical embodiment of the method and apparatus for the detectionof icontaminating'gases of this invention it will be -understood that the speci ficfldetails of construction and arrangement of parts as 'shown and described are by way of illustra: tionand are "not to be construed as limiting the scope of the invention; 7

Whatis claimed is: V I V a r 1. A contamination detector fora sealed transparent container -having a gaseous fil l'inc luding;a sour c e of high frequency energy'for producing ,a glow discharge within, said transparen t container, photo-detecting means di; rected to intercept lightemanating from said 'transparent container-incident -to-;said glow discharge, a bridge cir;

' cepted light.

cuit including a null detector and first and second measuring'arms; means-for-applying the output of said photo- 7 detecting means alternately to said first and second measuring arms, and means interposed between said transparent container and said photo-detecting means for differentially filtering said intercepted light to provide light output in alternation to said photo-detecting means yielding a measure o f the' ultra-violet content 0f;:Said inter- 2. A contamination detectorflfor'a sealed-bulbghaving a saswus'fill n lu i u c pfh t e usacy r y arranged to produce agaseousdischarge,within saictbnlb, a single photomultiplier tube directed at a selected field within said .-,-bulh2 to intercept-light emanatingltrom -said bulb incident to said, gaseoussdischarge said intercepted light having a band indicating the presence of air con- 7 tamination in said gaseous discharge, a comparison circuitincludinga null detector and first. and second meas- 'uring arms, means for applying the output of said 1photo-,

multipliertube alternatelytozsaid first and second rr1 e as,- uring arms'of said comparison circuigland meansinterposed between said bulb and ..said .tphotomultiplie'if v tube 1 for differentially filtering said intercepted light with respect'tosaid 'bandto provide. light ,outputin alternation to said photomultiplier tube yielding al measure-Dime, .7

presence of said band in said intercepted light 7 3: A, device for detecting air contamination of a,sealed bulb having a gaseous fill including a source of high fr qu y energy o pr d i aea rous .disch r ew thiul...

said bulb, photo detecting means responsivehto the light;

produced by said gaseous, discharge andiproduc g asignal output dependent upon the' ,spect r a1 g charactert ot said-gaseous discharge, the spectrum of said gaseous dis;-; charge having a band proportionedtto and indicativpf, the presence of air contamination within said sealed bulb signal-comparison 7 means, means for applying said signal output of sa'id photo-detecting means to saidj signal com parison means, and means: interposed between said bulb,v and said photo-detecting neans forfiltering t h e light pro duced by said gaseous ,discharge to provide light output in alternation tov said photo-detecting meanstyieldingga measure of said intercepted light 4; A device for detecting airtcontarnination ina sealed:

bulb having a gaseousfill comprisinga source of high frequency energy forproducing a gaseops discharge with}, in .said bulb, photo detecting means responsiue ltohthen.

light produced by said gaseous discharge andproducing q a signal output dependentupon the spcctlalcharacter ofr, said gaseous discharggthe spectrum of said gaseous dis-',. charge having a band proportional tou andindicative, of; the presence of air contamination within said,sealed.bulb,,,t signal-comparison means, means for, applying thev signal, output of said photo-detecting eans totsaid signalvcom-. parison means, and meansfonfilteringthe lightproduced by said gaseous dischargetin advanceoflsaid photo-detectv ing means to proyide light outputltosaid photoedetecting means in alternationwhich upon comparisonproducedar voltage proportional to and indicative, of thelpresence. of air contaminationwithinsaid sealed bulb 5. The method of testing bulbs having a,gaseousmfilll, for air contamination includingthe steps; of producingta,

glow. discharge within said bulb, iphotoelectrically measure ing the amount of yisible light in said glowldischarge to; obtain a first signal, measuring the total tlight aoutp'uti of, said ,gl ow discharge to obtain a second ,signal, balancing said signals against each othento, obtain a ,third. signal 7 indicative of theultra violet contentin said glowdisz,

charge as a measure of air contamination of said gaseons fill, n r je ting b lbsnindic tive oftex essivecontami tiqua qmpar dfto a sign lrofjknqwnyalue adap dast charge to obtain a first signal, measuring the total light output of said glow discharge to obtain a second signal, and balancing said signals against each other to obtain a third signal indicative of the ultra-violet content in said glow discharge as a measure of air contamination of said gaseous fill.

7. The method of testing bulbs having a gaseous fill for air contamination including the steps of producing a glOW discharge within said bulb, photoelectrically measuring the ratio of visible light in said glow discharge to the total light output of said glow discharge to obtain a signal indicative of the ultra violet content in said glow discharge as a measure of air contamination of said gaseous fill, and rejecting bulbs yielding a signal indicative of excessive contamination.

8. In apparatus for measuring the concentration of air within an enclosed space having a gaseous fill, means for producing a glow discharge within said enclosed space, a photo tube positioned to intercept light rays emitted from said enclosed space, filtering means interposed between said enclosed space and said photo tube for intermittently filtering out any ultraviolet radiation emitted from said enclosed space whereby said photo tube provides one current component corresponding to the total light output of said glow discharge and a further current component corresponding to the visible light output of said glow discharge, a measuring circuit, and switch means operable in substantial synchronism with said filtering means and connected between said photo tube and said measuring circuit and arranged to apply said one current component and said further current component to said 6 measuring circuit to obtain the ratio of said total light output to said visible light output.

9. In apparatus for measuring the concentration of air within an enclosed space having a gaseous fill, means for producing a glow discharge within said enclosed space, a photo tube positioned to intercept light rays emitted from said enclosed space, a rotatable drum having filtering means interposed between said enclosed space and said photo tube for intermittently filtering out any ultraviolet References Cited in the file of this patent UNITED STATES PATENTS 1,628,256 Machlett May 10, 1927 1,726,318 Sharp et a1 Aug. 27, 1929 1,963,185 Wilson June 19, 1934 2,316,344 Lemmers Apr. 13, 1943 2,484,323 Sweet Oct. 11, 1949 2,505,316 Wilmotte et a1 Apr. 25, 1950 2,527,122 Heigl et a1. Oct. 24, 1950 

